This invention relates to methods of producing thermistor chips which may find use in temperature compensating circuits and temperature detecting elements.
FIG. 8 shows an example of a prior art thermistor chip 41 of this type disclosed in Japanese Patent Publication Tokkai 7-74006, characterized as comprising a thermistor body 42, outer electrodes 43, inner electrodes 44 and a surface electrode 45. The thermistor body 42 comprises a semiconducting ceramic material having oxides of Mn, Ni and Co as its main component. The outer electrodes 43 are formed on mutually opposite end parts of the thermistor body 42. The inner electrodes 44 are formed inside the thermistor body 44 and each electrically connected to a corresponding one of the outer electrodes 43. The surface electrode 45 is formed on one of the surfaces of the thermistor body 42 and is separated from the outer electrodes 43.
The resistance value of the thermistor chip 41 is adjusted by trimming the surface electrode 45, say, by exposing the surface electrode 45 to a laser beam to form a groove 45c and thereby obtaining trimming electrodes 45a and 45b. A thermistor chip of a desired resistance value is thus obtained.
If prior art technology is used for this process, however, the thermistor chip is heated up by the energy of the laser and the thermistor body generates small cracks, causing variations in the resistance values of thermistor chips after the trimming process. Another problem with this prior art technology is that a laser beam must be made incident individually on each of many thermistor chips to be produced for trimming. This means that the process is cumbersome to carry out and contributes to an increase in the production cost.